A “camera module” is an assembly for housing optical elements and image sensing apparatus for use with a digital image sensor and devices incorporating such sensors. An example of a typical camera module is shown in FIG. 1, in an exploded view. The camera module comprises a barrel 10 and a mount 12. The barrel 10 is for carrying optical elements, for example, articles for refracting and/or reflecting light, such as lenses. The optical elements are emitted from FIG. 1 for the purposes of clarity of illustration. The mount 12 is for receiving an image sensing element (or elements) 14 for the conversion of incident radiation to an image. For a digital camera, the image sensing element 14 can be a digital image sensor such as a CMOS or COD integrated circuit.
The camera module comprises, as its basic components, the barrel 10 and the mount 12. In an assembly line, optical elements are affixed to the barrel and image sensing elements 14 are affixed to the mount 12, the barrel 10 is fitted onto the mount 12, and the resultant manufactured product is referred to as a “camera module”. For the purposes of the present application, the term “camera module” may be taken as being applicable equally to the barrel 10 and mount 12 components alone (either separately or assembled together), or to the complete assembled product comprising the barrel 10, optical elements, mount 12 and image sensing apparatus 14, together with other ancillary components which may be incorporated for different specific applications.
The camera module can then be incorporated into a printed circuit board (PCB) forming part of a digital camera. The image sensing apparatus 14 can be provided with input and output electrical contacts which receive command signals and output image data respectively. Depending on the application, different image processing functions can be carried out within the image sensing apparatus 14, or can be carried out by other circuitry in the PCB.
It is common for the barrel 10 and the mount 12 to be engageable with a screw thread, which in the example of FIG. 1, would be provided on the outer surface of the barrel 10 and an inner surface of the mount 12. The barrel 10 can be rotated with respect to the mount 12 during manufacture to adjust the position of the optical elements carried by the barrel 10, thereby setting the focus of the image sensor. For adjustable focus devices, further rotation may be carried out at the behest of a user on a manual or automatic basis.
The rotation, either during or after manufacture, may generate frictional forces because of the motion of the barrel with respect to the mount, which may cause some degradation of the barrel 10 and/or the mount 12 resulting in the generation of debris, known in the art as foreign matter (FM). The debris falls onto the image sensing apparatus and results in a loss of image quality, as the FM blocks incident radiation, and thus results in the loss of image data. This loss of image data can cause a significant number of assembled camera modules to fail quality checks performed at the end of the manufacturing process, or, for adjustable focus devices, causes image degradation after manufacture.